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Theses and Dissertations Graduate School

2010

Factors Affecting Gingival Excess, Altered PassiveEruption and Recession in the MandibularAnterior and Premolar SitesWilliam BohlenVirginia Commonwealth University

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Recommended CitationBohlen, William, "Factors Affecting Gingival Excess, Altered Passive Eruption and Recession in the Mandibular Anterior and PremolarSites" (2010). VCU Theses and Dissertations. Paper 2213.

Virginia Commonwealth University

This is to certify that the thesis prepared by William F Bohlen entitled FACTORS AFFECTING GINGIVAL EXCESS, ALTERED PASSIVE ERUPTION AND RECESSION IN THE MANDIBULAR ANTERIOR AND PREMOLAR SITES has been approved by his or her committee as satisfactory completion of the thesis requirement for the degree of Master of Science in Dentistry Thomas Waldrop, DDS, MS, Virginia Commonwealth University

John Gunsolley, DDS, MS, Virginia Commonwealth University

Harvey Schenkein, DDS, PhD, Virginia Commonwealth University

Robert Sabatini, DDS, MS, Virginia Commonwealth University

Harvey Schenkein, DDS, PhD, Virginia Commonwealth University

David C. Sarrett, DDS, MS, Interim Dean of the School of Dentistry, Virginia Commonwealth University

Dr. F. Douglas Boudinot, Dean of the Graduate School August 2, 2010

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© William F. Bohlen

All Rights Reserved

ii

FACTORS AFFECTING GINGIVAL EXCESS , ALTERED PASSIVE ERUPTION AND RECESSION IN THE MANDIBULAR ANTERIOR AND PREMOLAR SITES A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry at Virginia Commonwealth University.

by

WILLIAM F. BOHLEN D.M.D., Medical University of South Carolina

Director: Thomas Waldrop, DDS, MS Program director, Department of Periodontics, Virginia Commonwealth University

Virginia Commonwealth University Richmond, Virginia

August, 2010

iii

Table of Contents Page

List of Tables ................................................................................................................... 22

List of Figures ................................................................................................................... 29

Chapter

1 Introduction ........................................................................................................... 1

2 Methods and Materials...................................................................................... 6

3 Results ............................................................................................................... 9

4 Discussion ....................................................................................................... 13

5 Conclusion ...................................................................................................... 19

References ......................................................................................................................... 30

iv

List of Tables Page

Table 1: Demographic Information................................................................................... 20

Table 2: Periodontal Parameters ....................................................................................... 21

Table 3: Cast measurements.............................................................................................. 22

Table 4: Significance of Variables Affecting W:L, Length and Width ............................ 23

Table 5: Effect of Biotype on W:L ................................................................................... 23

Table 6.Effect of Gender on W:L ..................................................................................... 24

Table7: Effect of tooth type on W:L……………………………………………………..24

Table 8: Wheeler’s Average Lengths, Widths and W:L…….…………………………...24

Table 9: Gingival Parameters…………………………...………………………………..25

Table 10: Influence of Biotype on Recession, KT and age………..……………………..26

Table 11: Subjective Appearance of Gingival Excess and effect on W:L……………….26

List of Figures Page

Figure 1: Appearance of Mandibular Gingival Excess with thick Gingival Biotype.......27 Figure 2: Recession of Gingival Tissue with thin Gingival Biotype…………… … ......28 Figure 3: Normal Gingival Appearance with thin Biotype…………………………….. 29

v

Abstract

FACTORS AFFECTING GINGIVAL EXCESS, ALTERED PASSIVE ERUPTION AND

RECESSION IN THE MANDIBULAR ANTERIOR AND PREMOLAR SITES

By William F Bohlen, D.M.D.

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry at Virginia Commonwealth University.

Virginia Commonwealth University, 2010

Major Director: Thomas Waldrop, DDS, MS Program director, Department of Periodontics, Virginia Commonwealth University

AIM: The aim of this study was to determine the factors affecting gingival excess,

altered passive eruption and recession. METHODS: 100 subjects were examined

clinically and models of their mandible were fabricated. Demographic, periodontal and

cast measurements were recorded for each subject. Measurements were made on casts

with digital calipers and included clinical crown length, clinical crown width, papillary

height and gingival width. The W:L ratio was calculated and the proportion compared

to the maxillary arch ideal of .80. Values greater than .80 were used as a cutoff point

for defining gingival excess. Measures of periodontal health were also examined and

included probing depths, clinical attachment loss and bleeding on probing. Other

patient variables examined were history of orthodontics, presence of occlusal and

vi

incisal wear, presence of parafunctional habits, subjective appearance of gummy smile

and biotype. RESULTS: The mean W:L ratio was found to be 79.6 %. Tooth type

(p<0.001), gender (p<0.0237) and biotype (p<0.0081) were found to significantly

contribute to a W:L ratio >.80. There was a significant correlation between the

subjective appearance of gingival excess and the W:L ratio, regardless of biotype.

There was no association between recession and gingival excess. CONCLUSION:

Subjectively, 17% of the study subjects had gingival excess. When the author (WB)

made the determination that gingival excess was present, there was a significant

increase in the W:L ratio for all teeth, regardless of biotype versus teeth without the

presence of gingival excess. Proposed ideal W:L ratios for the mandibular anterior

teeth from the second premolar to central incisor are listed in Table 11.

This document was created in Microsoft Word 2007.

1

Introduction

One of the detractors from optimal smile esthetics is a “gummy smile”. The presence of a

gummy smile is due to factors predominately related to the maxillary arch, since it is the

more visible of the arches in a smile in most patients. In a “gummy smile,” a patient

shows excess maxillary gingival tissue for a variety of factors including vertical maxillary

excess gingival tissue, incisor overeruption of maxillary incisor teeth, gingival overgrowth,

short or hyper-mobile upper lip (high smile line) and altered passive eruption1. For this

reason, studies of smile esthetics have focused on the maxillary arch. The same factors

have not been studied in the mandibular arch.

This study will examine the variables that may contribute to excessive amounts or a lack of

gingival tissue in the mandible. Among these variables are the gingival widths of

keratinized tissue, gingival biotype and altered passive eruption. By examining how these

variables interact with each other, the appearance of excess gingival display in the

mandibular arch and overall gingival health may be investigated.

One of the most important factors related to excess gingival tissue is altered passive

eruption (APE). Altered passive eruption refers to an aberration in the eruption pattern of

teeth that results in excessive gingival display. Tjan15 found the prevalence of APE to be

present in 7% of men and 14% of women in both maxillary and mandibular arches, while

Volchansky16 found the prevalence in both arches to be around 12% in a population with a

mean age of 24.2 years of age. APE was first described by Gottlieb and Orban17 and it

involves migration of the gingival apparatus apically. Coslet18 developed a classification

system for APE of both the maxilla and mandible that defined two types of passive

eruption. The first form, Type 1, is defined as location of the gingival margin at an incisal

or occlusal position relative to the CEJ, with the mucogingival junction at a level apical to

2

the alveolar crest. Type 2 is defined by the presence of a normal gingival margin to

mucogingival junction width with the mucogingival junction located at or near the CEJ.

These two groups are then subdivided into A and B subtypes. The A subtype, delayed

passive eruption, is defined as a “normal” CEJ to alveolar crest distance of 1.5-2 mm. The

B subtype, arrested passive eruption, is defined as having an alveolar crest at the level of

the CEJ. In the delayed variety, a normal “biological width” is established according to the

mean dimensions described by Gargiulo et al.19, of .69 mm for sulcus depth, .97 mm for

epithelial attachment and 1.07 mm for connective tissue attachment. In the arrested form,

there is a junctional epithelial attachment on enamel, which can result in the appearance of

shorter clinical crowns. For that reason the length and width of the clinical crown have

been used as a possible predictor of altered passive eruption.

Wheeler21 described the average width of crown, width of cervical diameter, length of root,

and length of crown measurements of extracted mandibular incisors, canines and

premolars. The average length of the crown was 9 mm for a mandibular central incisor,

9.5 mm for a lateral incisor, and 11 mm for a canine. The first premolar was 8.5 mm and

the second premolar was 8 mm. The crown widths at the widest point were 5 mm for the

mandibular central incisor, 5.5 mm for the lateral incisor, 7 mm for the canine, 7 mm for

the first premolar and 7.5 mm for the second premolar. It should be noted that these

values represent the length and width of the enamel on teeth, but are not measures of the

visible clinical crown in a mouth. Due to the position of the attached gingival tissue in a

normal case, the actual clinical crown in the normal case would be shorter than the length

of the enamel by dimensions of the epithelial attachment plus the sulcus depth which add

to approximately 1.66 mm, according to Gargiulo19. In the case of altered passive

eruption, the clinical crown would be further shortened, providing a possible measure of

the occurrence of altered passive eruption.

The appearance of gingival excess can be created by factors other than altered passive

eruption. The width of the gingival tissue itself may be unusually large. Gingival width or

3

the measurement from the free gingival margin to the mucogingival junction (MGJ),

provides a measure of the amount of keratinized tissue apical to the tooth. The gingival

width is greater in males than females3 and increases as patient’s age and teeth continue to

erupt, resulting in decreased probing depths4. The gingival width also increases as a result

of continual apical deposition of cementum as a compensatory response to incisal wear5.

Bowers6 found that the average width ranges from 1-9 mm and that, within the mandible,

the canine and premolars tend to have less keratinized tissue width than the incisors. This

investigation sought to answer the question of whether, or not, gingival width has an effect

on APE or gingival health.

While excess gingival tissue may be viewed as a negative factor to esthetic appearance, it

may also have a positive effect on gingival health. One of the indicators of gingival health

in the mandible is the absence of recession. Kennedy and Bird7 followed 32 patients with

areas of recession and no keratinized tissue over 6 years and found that with adequate

plaque control, they were able to prevent further attachment loss. Wennstrom8 used beagle

dogs to show that if all keratinized tissue was removed and adequate plaque control was

achieved, further recession could be prevented over 4 months post-operatively. In contrast

to these findings, Lang and Loe9 felt that 2 mm of keratinized tissue was necessary for

health and resistance to recession, regardless of level of oral hygiene. For that reason the

amount of keratinized tissue present, on a tooth by tooth basis, will be investigated in order

to ascertain its effect on gingival health in terms of resistance to recession or contribution

to APE. The amount of keratinized tissue present is independent of the location of the

gingival margin in relation to the crown. There may be certain instances where there is

keratinized tissue present in an area of recession and vice versa. Alternatively, there may

also be areas with APE and differences in amount of attached tissue.

Gingival thickness is another variable that has been associated with both excess gingival

tissue (APE) and gingival health. Goaslind10 found that the average mean thickness of

keratinized gingiva was 1.44 mm with the average free gingival thickness measuring 1.56

4

and the attached gingiva measuring 1.25 mm. Muller11 examined the thickness of

mandibular gingiva in a population of forty 19 to 30 year-old males and females and found

that females had significantly thinner gingiva than males. Also, on average, the thickness

of the gingival tissue on the buccal surface of the mandibular central incisor was .7 mm

thick and the mandibular lateral tissue was .9 mm thick, indicating intra-arch variation in

the thickness. It is generally accepted that when comparing thick versus thin gingiva, the

thicker gingiva is better able to resist insult from plaque biofilm and therefore less likely

to break down, resulting in decreased gingival width and likelihood of recession. In both

human and animal studies, gingival thickness has been shown to be critical in the

prevention of mandibular incisor recession as a result of buccal tooth movement during

orthodontic treatment. Melsen12 found that the only variable associated with risk for

gingival recession in mandibular incisors subjected to orthodontic tooth movement was

thin tissue. Wennstrom’s13 monkey study, in which maxillary teeth with varying widths

and thicknesses of keratinized tissue were subjected to buccal orthodontic forces over 3-4

months, showed that the most important factors for recession development were plaque

presence and thin tissue. Width of keratinized tissue had no effect on the development of

recession. The data therefore shows that thick gingiva is better suited to resist the

development of recession.

The effect of biotype on excessive gingival tissue and/or APE will also be examined in this

study. Biotype is a genetically determined trait and it can be thin or thick. Most often it

refers to the gingiva, but it also includes the underlying bone. The alveolar bone and

gingiva do not necessarily have the same biotype. De Rouck14 conducted a study in which

gingival biotype was correlated with varying degrees of gummy smile. The presence of

APE was determined by examining the ratio of width to length for the maxillary central

incisor. A larger number indicated a “gummier” smile. Biotype was categorized by

documenting the transparency of the periodontal probe through the gingiva. Thinner

biotypes allowed the probe to be easily visible, while thicker biotypes obscured the

appearance of the probe. De Rouck examined maxillary central incisors in a group of 50

5

males and 50 females and then calculated the crown width to length ratio for all of the

teeth, correlated this proportion with the biotype, and found that there were three clearly

defined groups. Group 1 (n=37) had a crown width to length ratio of .79 and a clear, thin

biotype. Of these 37, 28 were female. The second group (n=34) had a .77 crown width to

length ratio and thick, clear biotype. The third group (n=29) had a crown width to length

ratio of .88 with a thick gingival biotype. These results suggest that a thick biotype can be

a contributor to gingival excess and therefore offer some protection from gingival

recession. The effect of biotype on gingival excess in the mandible will be investigated for

the first time in this study.

The primary purpose of this investigation is to determine the factors that contribute to

gingival excess and recession. Secondary objectives are to correlate subjective appearance

of gingival excess to width-to-length ratios and to establish “ideal” width-to-length ratios

for the mandibular anterior teeth and premolars. By determining the variables associated

with gingival excess and recession, prognostic value can be placed on them and future

changes in gingival health may be more easily predicted.

6

Methods and Materials

One-hundred healthy, non-smoking adult subjects were recruited from the Virginia

Commonwealth University School of Dentistry by e-mail notification and word of mouth

to participate in the study. Participants were warned of any potential risks and were

compensated for their time. No attempts were made to recruit patients specifically for the

presence of altered passive eruption.

The inclusion criteria included subjects having all mandibular central incisors to second

premolars with bilateral occlusal contacts. This eliminated the possibility of supraeruption

presence that would lead to inaccurate crown length measurements. All of the subjects

were older than 18 years old.

The exclusion criteria included pregnancy, active periodontal disease (BOP and CAL of 4

mm or greater), systemic conditions that could modify the progression or treatment of

periodontal disease (e.g. Diabetes mellitus), history of periodontal surgery in the area being

studied, missing teeth in recorded areas, history of drugs that could contribute to gingival

overgrowth (anticonvulsants, calcium channel blockers, immunosuppressants), poor oral

hygiene (evidence of gross supragingival plaque and calculus), current or past smoking (10

cigarettes or more per day) and previous mandibular esthetic crown-lengthening or

gingival grafts.

Informed consent was obtained under a procedure approved by the Institutional Review

Board (IRB) of Virginia Commonwealth University for research involving humans. IRB

approval was obtained prior to the initiation of this investigation.

Periodontal Exam

7

A clinical examination was carried out by a periodontal clinician (WB) and data were

recorded. Patients’ self reported age, gender, and race were recorded. Periodontal

conditions were measured with a standardized UNC probe from #20 to #29. The

periodontal conditions measured included sulcus depth (SD), gingival index (GI)12, plaque

index (PI)12 , clinical attachment levels (CAL) and bleeding on probing (BOP) and were

recorded at three facial sites per tooth.

Cast Measurements

Subjects had impressions made of their mandibular arch with alginate, and stone models

were fabricated. Measurements were made with a digital caliper and were made from teeth

#20 thru #29 on dental stone models. The crown length was measured from the free

gingival margin to the incisal or occlusal edge. The crown width was measured from the

mesial height of contour to the distal height of contour. Papillary height was also recorded

and was measured as a distance from a line drawn tangentially to the most apical portion of

the gingival scallop to the papilla tip. The distance from the gingival scallop of the

mandibular lateral incisor to the gingival esthetic line (GAL) was also documented.

Gingival width was also measured as the distance from the free gingival margin to the

mucogingival junction (MGJ). Gingival width was only measured on 85 of the casts

because the MGJ was only discernible on 85 of the models. Clinical crown width-to-

length ratio (W: L) was calculated from the average clinical crown length and average

clinical crown width measurements of each tooth type. These measurements were

compared to the ideal of .80 width-to-length ratio of maxillary teeth as previously reported

by Konikoff20 in the maxillary arch. Any measurement > .80 was considered to possibly

have altered passive eruption. This .80 value was an arbitrary value because it has not

been shown to have any value or relevance in the mandible. It was used as a baseline

number because it has been shown in the maxilla in numerous studies to have relevance.

Subjective information was recorded and included history of orthodontic treatment,

presence of parafunctional habit, presence of incisal or occlusal wear, overall appearance

8

of mandibular gingival excess, biotype (measured according to De Rouck14, by examining

the straight buccal of the central incisors) and whether or not symmetry present between

right and left sides was present.

The appearance of gingival excess was measured by evaluating the patients’ mandibular

teeth prior to the clinical exam. The appearance of gingival excess of the mandibular arch

was a subjective determination and was recorded by (WB) as either present or absent.

Analysis

Descriptive analysis was performed for this study on variables pertaining to demographic

data, presence of thick/thin biotype, all cast measurements of width and length, periodontal

parameters (probing depths, clinical attachment levels, recession, mucogingival width,

amount keratinized tissue) and percentage of patients with subjective appearance of

gingival excess and their corresponding width-to-length ratios.

In order to determine the influence that variables such as biotype had on width-to-length

ratio, logistic regression was performed with the arbitrary maxillary “ideal” of .80 width-

to-length set as the response variable.

When the response variable was continuous, data were analyzed with repeated measures

analysis of variance by tooth type to determine which variables were related to keratinized

tissue and recession. Keratinized tissue and recession were the continuous response

variables evaluated in this manner and the independent variables in the model were age,

gender, race, whether or not the individual had orthodontic therapy, had occlusal wear or

had the appearance of “gummy smile”.

Repeated measure analysis of variance, logistic regression and Fisher’s exact test were also

performed in order to determine which variables were significantly related to presence of

altered passive eruption and recession.

9

Results

One hundred dental students at the Virginia Commonwealth School of Dentistry were

examined and models were taken of their mandibular arches according to the previously

mentioned criteria. The subject population consisted of 39 females and 61 males with an

average age of 25.91 years of age. Thirty-nine of the subjects reported a history of

orthodontics and 67 subjects reported having a parafunctional habit (Table 1). Sixty of the

subjects were recorded as having a thick biotype (Table 1).

When the individual tooth lengths were estimated, it was found that the average lengths for

tooth types were 8.01 mm for mandibular central incisors, 8.24 mm for the lateral incisors,

9.45 mm for canines, 8.09 mm for first premolars and 7.10 mm for second premolars.

Average widths for the same teeth were 5.26 mm for the central incisors, 5.84 mm for the

lateral incisors, 6.73 mm for the canines, 7.06 mm for the first premolars and 6.94 mm for

the second premolars (Table 3).

When the width-to-length ratios were calculated, the values ranged from 67% for the

mandibular central incisor to 99% for the mandibular second premolar (Table 3). The

findings of this study also indicate that the mean width-to-length ratio for the mandibular

arch is 79.6%, which is consistent with the 80% arbitrary threshold that has been used in

studies of the maxillary arch as a possible indicator of APE. When the width-to- length

10

ratio was examined for individual teeth, it was found that 92% of mandibular second

premolars had an 80% or greater width-to- length ratio, with a mean of 99% width-to-

length ratio. In contrast, only 9% of mandibular centrals exhibited an 80% or greater

width-to-length ratio with a mean value of 67% width-to- length ratio (Table 3).

When the association between width-to-length ratio and factors such as age, presence of

occlusal wear, presence of parafunctional habits, history of orthodontics, gender, tooth

type, race, symmetry and biotype were examined, only tooth type (p<0.001), gender

(p<0.0237) and biotype (p<0.0081) were found to be significant (Table 4). In regards to

biotype, a thick biotype was significantly more likely to have a higher width-to-length ratio

when compared to a thin biotype ( 84.89% W:L ratio for thick, 80.15% for thin)(Table 5.)

For gender, females were significantly more likely to have a higher width-to-length ratio

(84.77% W:L ratio) than males (80.27% W:L ratio) (Table 6). For tooth type, the

mandibular second premolar was significantly more likely, when compared to the mean

width-to-length ratio of 79.6%, to have a width-to-length ratio>.80 (102% W:L ratio)

(Table 7). In regards to biotype, a thick biotype was significantly more likely to have

altered passive eruption when compared to a thin biotype ( 84.89% W:L ratio for thick,

80.15% for thin).

In order to determine how variables such as biotype might affect the average clinical length

of the teeth, repeated measures of variance were performed. It was found that the factors

(tooth type, gender and biotype) were also related to shorter lengths for the teeth,

11

indicating that they may play a role in contributing to short clinical crowns and a diagnosis

of altered passive eruption. The mean length of the mandibular teeth in the study was 8.18

mm and second premolars were shorter than this (average premolar length was 7.04 mm).

For gender, females had an average clinical crown length of 7.79 mm, which was

significantly shorter than their male counterparts (8.44 mm). Biotype was also shown to

have a significant association with clinical tooth length. Teeth with a thick biotype were

also found to be significantly shorter (7.86 mm) than teeth with a thin biotype (8.37 mm)

(Table 2).

When recession was examined on a tooth by tooth basis, it was found that the first

premolar had the highest mean amount of recession at 0.11 mm. The lateral incisor had the

lowest mean amount of recession at 0.02 mm (Table 9). When the amount of attached

tissue was examined for these same teeth, the mean value for the first premolar was 2.30

mm, while the mean amount for the lateral incisor was 3.33 mm (Table 9). When the

prevalence of recession was viewed on a tooth by tooth basis, 11% of first premolars had

recession, 10% of the second premolars had recession, 4% of the centrals had recession,

5% percent of the cuspids had recession and 1% of the laterals had recession.

When thin and thick biotype were analyzed according to presence of recession or mean

amount of attached tissue present, on a tooth by tooth basis, it was found that for the

central incisor, the presence of a thin biotype yielded a mean amount of recession of 0.11

mm. Alternatively, there was 0.00 mm of recession in patients with a thick mandibular

12

central incisor biotype (Table 10). For the central incisor, mean recession (repeated

measure analysis of variance) and the presence of recession (logistic regression and

Fisher’s exact test) were significantly related to biotype (P < 0.05) (Table 10). No other

tooth type was consistently related to recession by both statistical methods. For the first

premolar, biotype was significantly related to mean recession only (P < 0.05). There was

also a significant relationship between age and amount of keratinized tissue in the

mandibular central incisors and laterals. This was a positive correlation and as age

increased, the amount of attached, keratinized tissue increased as well (P <0.05) (Table10).

When the variables effecting the width of attached gingiva were analyzed (evaluated by

repeated measures analysis of variance) on a tooth by tooth basis, it was found that biotype

had a significant effect on width of attached gingiva (P<.0063)in the central incisor, with a

thick biotype having a mean width of 3.73 mm versus 2.66 mm for the thin biotype.

When the subjective documentation of appearance of gingival excess was compared to the

width-to-length values for the individual teeth, it was found that if the subjective

determination was made that gingival excess was present, the value for width-to-length

ratio increased to significant levels (Table 11). This was significant for all of the teeth

being studied and the significance was greatest for the first premolar, second premolar and

cuspid (all P<.0001), and less for the lateral (P<.0087) and central (P<.01).

13

Discussion

This study attempted to apply width-to-length proportions of teeth that are considered

“ideal” (.80) in the maxillary arch to the mandibular teeth. In the maxillary arch,

exceeding this ratio is a potential indicator of altered passive eruption and the prevalence

of maxillary altered passive eruption is considered to have a detrimental effect on smile

esthetics. The potential variables associated with this ratio were also analyzed in the

mandibular arch. Because the mandibular teeth and their gingival zeniths are rarely visible

upon smiling, the presence of mandibular altered passive eruption does not usually affect

esthetics, as in the maxilla. The current study sought to determine whether gingival

excess of the mandible may have some protective benefit from gingival insults which lead

to recession development.

The results of the current study indicate that the average width-to-length ratio was 79.6%,

which is consistent with the 80% threshold considered “ideal” in the maxilla for optimal

esthetics. This proportion should be viewed with some caution, as there has never been a

study to suggest that this is the optimal width-to-length ratio for mandibular teeth. Also,

when the width-to-length ratios were examined for the individual teeth, there were a wide

range of values from .99 for the mandibular second premolar to .67 for the mandibular

central incisor (Table 3). The mandibular centrals, laterals and canines were shown to

have lower width-to-length ratios than premolars. This observation is best explained by

their individual crown anatomies. The lengths of the mandibular centrals, laterals and

canines are proportionally larger than their widths, according to data collected from

extracted teeth by Wheeler21 (Table 8). On the other hand, the lengths and widths of

mandibular premolars are more similar and therefore yield a width-to-length proportion

closer to 1 (Table 3). When the width-to-length ratios from Wheeler’s study of extracted

teeth without gingiva are compared to the values from the current study, the results are

14

similar. The results were slightly higher for the current study, with variation in proportion

due to presence of gingiva and variation in the dimension and biotype of the gingival tissue

between subjects.

The variation in width-to-length values between Wheeler’s extracted teeth and those of the

current study were most likely due to a decrease in clinical crown length by the presence of

gingiva. The anatomical crown length was shortened by the presence of connective tissue

attachment, epithelial attachment and sulcus depth as proposed by Gargiulo19. The

consequent decrease in crown length created a higher width-to-length ratio and a

“gummier” appearance. The allowance for biologic width creates the shorter values for the

lengths versus Wheeler’s length data.

Subjects with a thick biotype were significantly more likely to have a width-to-length ratio

of .80 or greater. These data are in agreement with that of De Rouck14 who found that

thicker biotypes did have a larger width-to-length ratio of .88 versus .79 for thin biotype.

The current study found that thick biotypes had a mean width-to-length ratio of .85 and

thin biotypes had a mean of .80 (Table 5). Thicker biotype contributes to less crown

exposure due to its larger degree of “biomass” which results in shorter crown lengths.

This, in turn, leads to a larger width-to-length ratio.

Females had a significantly higher W:L ratio(Table 6) and this was due to a significantly

shorter overall clinical tooth length versus males. The shorter the length of the tooth, the

higher the W:L ratio. Tooth length, again, determined the W:L ratio.

The second premolar was also found to have a significantly larger width-to-length ratio of

1.02 (Table 7). This follows the trend of increasing width-to-length ratio from anterior

teeth to posterior teeth that was reported in Wheeler’s study (Table 5). His data showed a

mean width-to-length ratio of .94. The finding from the current investigation is not

15

surprising because the width and length of second premolar anatomical crowns in

Wheeler’s study are close to 1 without the presence of gingiva, as in Wheeler’s study.

When the gingiva is present, the cemento-enamel junction is often obscured by the free

gingival margin. This decreases the clinical length and increases the width-to-length ratio.

The most interesting finding of this study was the high degree of agreement between the

author’s subjective determination of the appearance of gingival excess and a significant

increase in width-to-length for all of the teeth being studied (Table 11). Subjectively, 17%

of the study subjects had gingival excess (Table 12). Fourteen of these subjects had

gingiva classified as thick and three classified as thin. For the subjective determination of

gingival excess, the most frequently viewed teeth were the mandibular centrals, laterals

and canines. The premolars are less visible from an anterior view and because of this, the

mandibular centrals, laterals and canines are the predominant determinants in the

appearance of gingival excess. The actual percentage of mandibular centrals with a width-

to-length ratio greater than .80 was determined to be 9%. For the mandibular lateral

incisors and canines, the values were 15% and 17 %, respectively. These values are very

similar to the 17% deemed subjectively to have gingival excess. For the mandibular first

premolar and second premolar, the percentages over the .80 width-to-length ratio were

78% and 92%, respectively. The importance of this finding is that it suggests that the eye

of the examiner was capable of determining that there was an excess amount of gingiva

present. This, in turn, provides some evidence that the threshold of .80 for defining the

“ideal” amount of gingival display can be extrapolated to the mandibular arch from the

maxillary study by Konikoff 20. In all fairness, the sample size was small, and although the

findings were significant, the question of whether or not mandibular gingival excess (APE)

needs treatment is another matter.

Values above the .80 width-to-length threshold were used to identify, non-invasively, the

presence of gingival excess. This measurement was not capable of leading to a diagnosis

16

of altered passive eruption because the author did not identify where the crest of bone was

relative to the CEJ. A true diagnosis of altered passive eruption would need to be

confirmed by examination of radiographs and surgical exposure during crown-lengthening.

The real question is: at what point is gingival excess (APE) so unesthetic that it needs to be

surgically corrected? This study does not address that question, but it does provide

evidence that the .80 width-to-length ratio might hold some applicability in the mandibular

arch for defining “ideal” (Table 11). The current study determined that the mean width-

to-length values for the mandibular centrals, laterals and canines are all close to the

arbitrary value of .80. The .80 value was used as a starting point because ideal values

don’t currently exist for the mandible. The mean value was .75 for the central, .81 for the

lateral and .78 for the canine for patients with thick biotype and the subjective appearance

of no gingival excess. The mean values for the first and second premolars were .98 and

1.13, respectively. Within this study, a subjective absence of gingival excess was used to

represent the ideal values. There was no statistically significant difference between

biotypes for subjective appearance of gingival excess and W:L ratio. This data provides

the first support for ideal values for width-to-length ratios for the mandibular anterior

teeth.

The differences between the width-to-length values between anterior and posterior teeth

can best be explained by differences in width-to-length ratio and tooth length. The anterior

teeth, when compared to the posterior teeth, are longer (Table 3) and have a smaller width-

to-length ratio. The findings of this study are supported by those of Ward23, who

conducted an online survey of dentists’ preference for width-to-length ratios. He used an

image of six maxillary anterior teeth and altered the lengths from very short to very tall.

He also created different width-to-length ratios by altering the location of the gingival

margin. The different width-to-length ratios examined were 62% (Golden Proportion),

70% and 80%. The preference for “ideal” by the dentists surveyed differed based on the

shape of the tooth. The 62% was preferred for tall teeth, while the 80% value was

17

preferred for very short/short teeth. The data from the current study seems to fit well with

these proportions. The central mandibular incisor, which is longer than it is wide, had a

width-to-length ratio of .67 for thick biotype and .63 for thin (Table 11) when the

subjective appearance of gingival excess was not present. The lateral incisor and cuspid

had similar values for width-to-length values (Table 11) and are also longer than they are

wide. The premolars had an increase in width-to-length value and also have a “shorter”

appearance. When it was felt that gingival excess was not present, the first premolar had a

width-to-length ratio of .87 for thick and .85 for thin biotype (Table 11). The trend,

therefore, within this study and that of Ward23 is that anterior and posterior teeth have

different shapes and therefore different ideal width-to-length ratios.

The differences in width-to-length ratio and subjective appearance of gingival excess

suggest that there may not be one fixed width-to-length proportion that can be applied to

all teeth in an arch. It follows then, that because the teeth within the mandibular arch have

different shapes, they also have different ideal width-to-length proportions. This is the first

data that puts forth preferences for ideal width-to-length values of mandibular teeth based

on subjective appearance of gingival excess.

The question of when surgery becomes necessary to improve esthetics might best be

answered by a combination of factors rather than a single proportion. The subjective

feeling for presence of gingival excess, comparison of width-to-length values to “ideal”

values and clinical documentation of variables such as location of CEJ in relation to bone

height, probing depth and amount of incisal wear present may all help to determine the

necessity for surgical intervention. This study can’t answer the question with any certainty

in terms of whether or not there is one “ideal” width-to-length ratio that must be achieved

for mandibular esthetics. What can be taken from this study is that the ideal is different for

every tooth, depending on factors such as tooth shape and location in the arch.

18

In terms of the question of whether or not APE provides protection from gingival insult,

the data seems to suggest that a patient with APE is not likely to have recession. However,

within the study there were subjects that did exhibit recession. In order to determine what

variables may have contributed to recession, logistic regression was performed. The

association between the amount of attached keratinized tissue, amount of recession and

probing depth were also evaluated. It was determined that a thin mandibular central

incisor biotype was significantly more likely to have recession (Table 10) versus a thick

biotype. The prevalence of recession in this study was lower than that documented in

previous studies such as Thomson’s examination of a birth cohort of 26 year-olds.

Thomson24 found that 70% of the population had at least 1 mm of recession. The

prevalence in this current study was most likely lower because only 10 teeth were

examined. If the entire dentition had been examined, the prevalence would most likely

have increased. Note that the prevalence of recession was low, most likely due to the mean

age of the study population at 25.91 years of age. Thus, these results must be viewed with

some caution.

Over time, one would also expect the percentage of recession to increase within this

population. A longitudinal, prospective study design that follows subjects with a thin

biotype over time would provide the strongest evidence of that. Because of the cross-

sectional nature of the current study, little predictive value as to the future development of

recession in the patients identified as having a thin biotype can be placed on the data.

19

Conclusion

The Mean age of the study population was 25.91 years of age. The lengths of teeth

were shorter than Wheeler’s21 extracted teeth due to presence of gingiva. The average

width-to-length ratio was 79.6% for the subject population

Subjects with a thick biotype were significantly more likely to have a width-to-length

ratio of .80 or greater (p<0.0081). Females had a significantly higher width-to-length

ratio (p<0.0237) versus males. In terms of tooth type, the second premolar was also

found to have a significantly larger width-to-length ratio of 1.02 (p<0.0001) versus the

other teeth. The lengths of the teeth were also significantly related to biotype, gender

and tooth type. Width of the teeth was only significantly related to tooth type.

For the central incisor, mean recession and the presence of recession were significantly

related to biotype (P < 0.05). For the first premolar, biotype was significantly related

to mean recession only (P < 0.05). Biotype had a significant effect on width of

attached gingiva in the central incisor (P<.0063), with a thick biotype having a mean

width of 3.73 mm versus 2.66 mm for the thin biotype. Biotype also had a significant

effect for attached gingival width of the lateral incisor, with thick biotype having a

mean width of 3.81mm and thin 2.95 mm.

Subjectively, 17% of the study subjects had gingival excess. When the author (WB)

made the determination that gingival excess was present, there was a significant

increase in the W:L ratio for all teeth, regardless of biotype.

20

Tables

Table 1. Distribution of subject Demographic Variables: Gender, Race, History of

Orthodontic Treatment, Presence of Parafunctional Habits, Presence of Incisal and

Occlusal Wear and Gingival Biotype

Gender

N Percentage

Male 61 61%

Race

African American 2 2%

Asian 16 16%

Caucasian 72 72%

Hispanic 4 4%

Other 6 6%

Orthodontic Treatment

Yes 61 61%

Parafunctional Habits

Yes 67 67%

Occlusal/Incisal Wear

Yes 95 95%

Biotype

Thick 60 60%

Thin 40 40%

21

Table 2. Periodontal Measurements and Indices according to Tooth Type: Pocket

Depth (PD), Clinical Attachment Loss (CAL), Bleeding on Probing (BOP),

Periodontal Index (PI), Gingival Index(GI)

2nd Premolar 1st premolar Canine Lateral Incisor Central Incisor

Mean SD Mean SD Mean SD Mean SD Mean SD

PD (mm) 1.31 0.51 1.30 0.50 1.23 0.46 1.23 0.45 1.16 0.39

CAL (mm) 0.21 0.60 0.27 0.69 0.17 0.72 0.07 0.32 0.12 0.46

BOP 0.01 0.11 0.02 0.14 0.02 0.15 0.02 0.15 0.02 0.15

PI 0.37 0.55 0.58 0.68 0.82 0.76 0.78 0.75 0.86 0.80

GI 0.23 0.43 0.35 0.49 0.54 0.57 0.61 0.59 0.58 0.57

22

Table 3. Cast Measurements: Width, Length, W:L , Percent over ideal W:L Ratio of

.80

2nd Premolar 1st premolar Canine Lateral Incisor Central Incisor

Mean SD Mean SD Mean SD Mean SD Mean SD

Width (mm) 6.94 0.64 7.06 0.55 6.73 0.47 5.84 0.47 5.26 0.46

Length (mm) 7.10 0.83 8.09 0.80 9.45 1.19 8.24 0.94 8.01 0.98

W:L 0.99 0.16 0.88 0.10 0.72 0.10 0.72 0.10 0.67 0.12

Percent over ideal W:L of

.80 0.92 0.28 0.78 0.42 0.17 0.37 0.15 0.35 0.09 0.28

23

Table 4. Significance of effect of variables on W:L , Width and Length

Table 5. Effect of Biotype on W:L Ratio

W:L Width Length

Age 0.6285 0.2112 0.6648

Occlusal wear 0.7403 0.3552 0.2898

Parafunction 0.8173 0.0816 0.1210

Orthodontics 0.4844 0.7672 0.5429

Gender *0.0237 0.0709 0.0001

Tooth Type *<0.0001 <0.0001 <0.0001

Race 0.3077 0.1557 0.2065

Symmetry 0.2520 0.8592 0.1675

Biotype *0.0081 0.8892 0.0007

Level Least Sq Mean Std Error THICK 0.849 0.027 THIN 0.802 0.029

24

Table 6. Effect of gender on W:L Ratio

Table 7. Effect of tooth type on W:L Ratio

Table 8. Wheeler’s21 Average W:L , Length, Width

Level Least Sq Mean Std ErrorF 0.84772144 0.02699896M 0.80279039 0.03043470

Level Least Sq Mean Std Error2nd Pre 1.02 0.0281st Pre 0.91 0.028Cuspid 0.75 0.028Lateral 0.747 0.028Central 0.697 0.028

Tooth W:L Ratio

Cervico-Incisal/Occlusal Length of Crown (mm)

Mesiodistal Crown Diameter (mm)

Central Incisor

.56 9 5

Lateral Incisor

.58 9.5 5.5

Canine .63 11 7

1st Premolar

.82 8.5 7

2nd Premolar

.94 8 7.5

25

Table 9. Gingival Parameters: Probing Depth, Clinical Attachment Level, Muco-gingival Width, Attached Tissue

2nd-Pre 1st-Pre Cuspid Lateral CentralPocket Depth N -

Patients 100 100 100 100 100

Mean 1.31 1.30 1.23 1.23 1.16 Std Dev 0.51 0.50 0.46 0.45 0.39Attachment level Mean 0.21 0.27 0.17 0.07 0.12 Std Dev 0.60 0.69 0.72 0.32 0.46Recession Mean 0.08 0.11 0.10 0.02 0.05 Std Dev 0.32 0.40 0.52 0.16 0.25 Muco – gingival width N 85 85 85 85 85 Mean 3.68 3.60 4.30 4.54 4.27 Std Dev 1.02 1.01 1.35 1.26 1.24Keratinized-Attached N -

Patients 85 85 85 85 85

Mean 2.36 2.30 3.07 3.33 3.14 Std Dev 1.10 1.10 1.35 1.19 1.20

26

Table 10. Influence of Biotype on amount of Recession, Keratinized Tissue and Age

*Significantly related to biotype and age ( p < 0.05). There was a positive correlation between age and keratinized tissue for the indicated teeth.

# For the central incisor, mean recession (repeated measure analysis of variance) and the presence of recession (logistic regression

and fisher’s exact test) were significantly related to biotype ( p < 0.05). No other tooth type was consistently related by both statistical methods.

$ For the first premolar biotype was significantly related to mean recession only (p< 0.05).

Table 11. Effect of Subjective Appearance of Gingival Excess on W:L Ratios for both thick and thin biotypes

2nd-Pre 1st -Pre Cuspid Lateral Central BIOTYPE_ Mean Std

DevMean Std

DevMean Std

DevMean Std

Dev Mean Std

DevRecession THICK 0.05 0.29 0.07 0.31 0.08 0.48 0.00 0.00 0.00 0.00 THIN 0.11 0.36 $0.16 0.49 0.13 0.58 0.04 0.25 #0.11 0.39Keratinized THICK 2.38 1.17 2.32 1.12 3.30 1.29 *3.57 1.13 *3.38 1.18 THIN 2.33 0.97 2.26 1.07 2.71 1.36 2.96 1.18 2.75 1.13Age THICK 26.32 3.02 THIN 25.30 3.00

2nd -PRE 1ST-pRE Cuspid Lateral Central BIOTYPE APP G

EXC N Mean Std

DevN Mean Std

DevN Mean Std

Dev N Mean Std

DevN Mean Std

DevTHICK NO W:l 46 0.97 0.13 46 0.87 0.09 46 0.71 0.09 46 0.72 0.12 46 0.67 0.14 YES W:l 14 1.13 0.25 14 0.98 0.09 14 0.81 0.09 14 0.78 0.07 14 0.75 0.05THIN NO W:l 37 0.96 0.12 37 0.85 0.09 37 0.69 0.09 37 0.69 0.08 37 0.63 0.09 YES W:l 3 1.12 0.14 3 1.00 0.09 3 0.81 0.07 3 0.78 0.09 3 0.67 0.03

27

Figures

Figure1. Appearance of Mandibular Gingival Excess with thick Gingival Biotype

28

Figure 2. Recession of Gingival Tissue with thin Biotype

29

Figure 3. Normal Gingival Appearance with thin Biotype

30

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